Juicy-lipped male frogs give females ‘love bites’ with pheromones

Love can literally be in the air when it comes to pheromones, but some species take matters into their own hands – or in their mouths – when it comes to making sure the chemical message hits their target. . Direct transmission of sex pheromones, as it is romantically called, is well documented in invertebrates, but it is a less common strategy used in animals with a backbone – that was until frogs pouting make their appearance.

New research published in the journal Frontiers in Zoology details the more direct approach taken by frog species from the Plectrohyla kind. It turns out that the males of these species engage in “traumatic mating” to improve their chances of reproductive success, using specialized teeth to effectively scratch their love scent in the females. And they say chivalry is dead.

It turns out that traumatic mating is not that uncommon in amphibians.

“Traumatic mating can be observed in many animal species,” lead author Lisa M Schulte told IFLScience. “Many species of frogs pierce females with thorns on their thumbs during ampexus. It is likely that this is also used for the transfer of pheromones.

Amplexus is a fancy word for the sex position that frogs and toads assume when mating, which sees the male hugging the female from behind. In this study, the researchers investigated whether the elongated teeth and swollen lips of men Plectrohyla frogs have also been used to transfer pheromones during traumatic mating.

The plump pout of Male Plectrohyla frogs are best admired from below. Image courtesy of Lisa M Schulte

To find out, they turned to experts in the field: mating pairs of frogs. Observation of the animals revealed that the males used their full lips to push off the backs of the females during ampexus. The action left small scratches behind, made by the frogs’ special teeth.

Samples of the plump frogs’ pout revealed that they contained specialized mucus glands that resembled those known to excrete pheromones in amphibians. Their purpose was confirmed by whole transcriptome sequencing, which showed proteins of the precursor-like factor of sodefrin, a pheromone known to amphibians.

However, pheromones perform many different behaviors (like swarming locusts) and there is currently not enough evidence of what these “love bites” actually achieve in frogs. They may speed up a female’s egg-laying time, Schulte says, but what sets this study apart is the species’ unique approach.

“We have already discovered before that several species of frogs have glands that contain potential pheromones,” said Schulte. “However, all of these species seem to transfer these molecules to the female’s nose. The most intriguing result of this study is that there appears to be a different path, where the pheromones are transferred [via skin]. “

The researchers then hope to better understand the effect of male pheromones on females during reproduction in frogs and toads.

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